The field of powdered of both metallic and non-mettalic articles has gained substantial prominence in relatively recent years owing to the development of new electrostatic coating powders capable of being subsequently heat fused at lower temperatures and shorter curing times. This type of protective coating offers many advantages over spray coating, including the effective utilization of as much as 95% of the powder materials as compared with a maximum of 60% in the case of wet painting. Energy consumption is markedly reduced, because one powder coat may be made as thick as required, and covers better and cures at lower temperatures than three or four wet paint coats. In the case of coating hollow articles, such as elongated length of pipe and the like, the ability to flow an air current carrying the powder through the bore of the pipe permits even coating in a manner substantially unobtainable by spray techniques.
At the present state of development of the art, there are various methods using electrostatically charged powder. The most widely used are those including an electrostatic generator, a high voltage spray nozzle, and a tank containing powder with a mechanical mixer. The process is carried out in a spray booth, and exposes personnel to the powder as it is sprayed, and the possibility of shock from the electrically powered components of the apparatus. Powder losses are comparable with material losses involved in spray painting, and unused powder is not easily reclaimed. Pollution of the surrounding atmosphere is substantial.